Meter relay



Feb. 26, 1946. F. G. KELLY v 2,39,s9

METER RELAY Filed May 13, 1942 '56 Sfmentoxtv Fvederck G. K any'Patented Feb. 26, 1946 METER RELAY Frederick G. Kelly, West Orange, N.J., assigner -to Thomas A. Edison, Incorporated, West Orange, N. J., acorporation of New Jersey Application May 13, 1942, Serial No. 442,760

Claims.

This invention relates to meter relays and more particularly to meterrelays of the DArsonval type.

Meter type relays employ meter movements as the actuating means. Sincemeter movements are characterized by high sensitivity, this type ofrelay is usually used where the available electric power is very small,such as in the cases Where therinocouples, photo-cells, magneticinductor pick-ups, etc. are the actuating or motive means. Metermovements however develop very small mechanical power, and seriousdiiculties have been encountered in utilizing that power to produce astable contact between the switch Contact points of the relay.

It has, for example, been the practice in DArsonval type relays to havethe movable contact point carried directly by the coil of the DArsonvalmovement and to have this Contact point to swing, as the coil isactuated on its pivots, into engagement with a substantially stationarycontact point which serves as a stop for the coil. Since designlimitations have required that the movable contact point be mounted at asubstantial radial distance from the pivot axis of the coil, the smalldeveloped torque of the coil has been eilective to produce only a verysmall contact pressurea pressure which has been frequently insufficientto break down or cut through the lm or dirt on the contact points tomake a good electrical connection. In addition, it is required that thecurrent connection to the contact point be made through one of thespiral torque springs of the coil or else through an additional spiralconducting spring, the connection through a spiral spring being requiredto provide a stable mechanical connection having small resistance t0movement of the coil. If the torque spring of the coil is employed forthis connection, the actuating circuit becomes connected to thecontrolled cir-` cuitwhich is a serious disadvantage in someapplications. Moreover, in either case there is the disadvantage thatthe value of current which the relay can control is limited to the smallcurrent conducting capacity of such spiral springs-which is typicallyabout .2 ampere.

In self-restoring DArsonval type relays thecoil is actuated against thereacting torque of a restoring spring, and each position reached by thecoil in response to a given value of actuating or energizing current isone, as until the contact points engage, wherein the actuating andrestoring torques are equalized. Thus, the coil is left at each suchposition with no immediate reserve capacity to do work. When thedeveloped reserve coil torque is utilized directly to produce a Contactpressurey as is above explained, the contact points tend to engageinitially with very small pressure. Moreover in view of the reversibleaction of the relay, in that the contact points will open and close atthe same value of actuating current, there is a tendency for the contactpoints to open and close erratically in response to slight variations inactuating current and from mechanical shock and vibration. Such erraticopening and closing of the contact points, or contact chatter, not onlydestroys the controlling action of the relay but also produces arcingand consequent heavy wear of the contact points,

In accordance with the present invention, the contact points are limitedto a minimum practical separation-a minimum required separation fordependable operation as determined by manufacturing tolerances and otherpractical considerations-and the coil of the meter movement is actuatedthrough a wide angle, as of the major part of a right angle, to effectthat minimum separation. This is done by means of a coupling means ormovement transmission between the coil and contact point or pointshaving a very small movement-transmitting ratio. This use of a couplingmeans having such small transmitting ratio enables the small actuatingtorque of the coil to control a much greater pressure between thecontact points, and thus to obtain a very improved degree of stabilityfor the relay.

By this arrangement vof my invention, the contact points are permittedto be mounted independently of the coil of the DArsonval movement. Thus,the need for spiral conducting springs for making the current connectionto the contact points is eliminated, the controlled circuit is readilyelectrically divorced from the actuating or coil circuit, and thecurrent controlled need be limited only by the contacts points of therelay. In addition, the capability of the movement to control a manytimes greater contact pressure permits the contact points to be mountedin sturdier fashion with consequent less susceptibility to erraticoperation from mechanical vibration or shock.

In accordance with the preferred construction of my invention, I providea cam transmission between the actuating coil and the switch contactpoints. The cam of this transmission is mounted directly on the shaft ofthe coil, while the contact points are mounted on cantilever-held springarms which bear against the cam from the opposite sides thereof towardstheir contact-closing positions. The cam transmission is arranged tohave a very small movement-transmitting ratio as is aforementioned, andaccordingly the spring arms are made quite stiff; moreover, the cam ismade over-critical to hold the springs constrained in open positionwhile the coil is in unactuated or zero position, without influence onthe coil of the reaction of the springs. By this construction, a falseclosing of the contacts from a mechanical vibration or shock of therelay is well-nigh impossible. This is true not only for vibration intranslation but also for vibration in rotation since a large angle ofdeflection of the coil is required to permit the contacts to close.

It is accordingly an object of my invention to improve the performanceand stability of operation of meter-type relays while preserving theirhigh sensitivity.

It is another object to provide a sensitive meter relay capable ofwithstanding heavy mechanical shocks and vibration.

It is another object to provide a sensitive meter n relay which iscapable of withstanding heavy vibration and substantial variations inactuating current without undergoing a false or erratic operation.

It is another object to provide an improvement in meter relays wherebyto effect a greater contact pressure.

Another object is to provide a stable DArsonval relay free from contactchatter or bouncing.

A further object is to provide an improved arrangement of the electricalcircuits of a DArson- Val type relay permitting a greater latitude ofcontrol and of efficiency of operation of the relay.

Other objects and features of my invention will more fully appear fromthe following description and the appended claims.

In the description of my invention reference is had to the accompanyingdrawing, of which:

Figure l is an elevational View of the mechanism of a DArsonval relayconstructed according to my invention;

Figure 2 is a plan view of the structure of Figure 1;

Figure 3 is a fractional plan view to enlarged scale showing therelative positions of parts of the relay mechanism when the contacts areheld in open positions;

Figure 4 is a fractional view showing the relation of the camtransmission to the contact springs when the contacts are closed; and

Figure 5 is an enlarged vertical sectional view showing details of thestructure to enlarged scale.

In the gures there is shown a relay employing a sensitive DArsonvalmovement generally referred to as I0. This DArsonval movement comprisesa permanent magnet in the form of a. curved bar magnet I I provided withflat side surfaces I2 near the ends. Clamped against the surfaces I2 byscrews I3 are respective pole pieces I4. These pole pieces terminateadjacent to one another into cylindrical faces I5 to form asubstantially complete cylindrical gap therebetween. Bridging the polepieces, at their sides adjacent to the permanent magnet, and securedthereto by screws I5, is an upstanding non-magnetic member l1 of abracket I8. This bracket has two depending legs I9 which are secured byscrews 29 to a fiat annular member 2i that forms a base for the relay.Staked into the central opening 22 of this base member is a short tube23 fractionally shown. This tube serves as a conduit through which thelead connections to the relay may pass. The structure is enclosed by acylindrical casing not shown which may have suitable connection to thebase member 2|.

Secured against the top sides of the pole pieces, by screws 24, are twodiverging members 25 of a non-magnetic bracket 2B, the central joiningpart of which depends down along the outer sides of the pole pieces.This bracket has a short horizontal arm 21 turned over between thediverging members 25 which terminates into a disk-shaped part 23.Secured to this part is a depending cylindrical soft iron core piece 29which is centralized between the cylindrical faces I5 to form an annularair gap 30 of constant length between the pole pieces; it is this gapwhich con stitutes the field for the DArsonval movement.

Surrounding the central core piece 29 is a rectangular coil 3I. Thiscoil has upper and lower shafts 32 and 33 which pivotally engagerespective jewel bearings mounted in respective screws 34 and 35. Thescrew 35 is threaded into a lug 31 which is turned over from the bracket26, while the screw 34 is threaded into a transverse bar 39 at the topof the movement, this bar being clamped to the pole pieces againstspacing washers 4D by the screws 24 aforementioned. 'I'he upper screw 34is to be adjusted to control the pressure of the jewel bearings againstthe coil pivots, but is locked in adjusted position by a lock nut 4I.

The coil is biased torsionally to a neutral or zero position, as againsta stop constituting the arm 21 abovementioned, by means of upper andlower spiral restoring springs 42 and 43. These springs are interposedbetween the coil and suitable respective anchors of which that for theupper spring is a pin 54 carried by the cross bar 39 and that for thelower spring is a member 55 clamped to the lug 31 by a nut 36 on thescrew 35. Due to the small torque which a DArsonval movement can developit is customary to make the lead `connections to the coil through therestoring springs 42 and 43. For this reason the springs are anchored torespective terminals of the coil, the terminal for the upper springbeing shown as 56. One lead connection is then made to a soldering lug51 provided on the member 55 and the other lead connection is made to asoldering lug 58 clamped between the bar 39 and one of the spacingwashers 40. For isolating the electrical circuits to the coil from theframe structure of the relay, the bar 39 is separated from the screws 24and spacers 40 by insulating washers 59, and the member 55 is separatedfrom the lug 31 and screw 36 by insulating washers 59.

When a D. C. voltage source is connected to the coil 3| and with theproper polarity, the coil will be actuated in a clockwise direction fromits zero position. The distance of angular movement of the coil will bein proportion to the value of the energizing current flowing through it,each position reached by the coil being one wherein the actuating torqueon the coil is substantially equal to the reaction torque of therestoring springs 42 and 43. For progressively larger values of currentthe coil will thus deflect to increasingly larger angles as to alimiting deflection of about In accordance with the present inventionthe major part of this angle of deection of the coil is utilized tocontrol the minimum contact-point separation above noted, as is nowexplained.

The switch means for the relay comprises a pair of spring contact arms44 held insulatedly in cantilever fashion in substantially radialrelation to the upper shaft 32 of the coil 3|. These springs are clampedto a bracket 45 between insulating plates 46, the bracket being in turnsecured to a flat arcuate member 41 which is mounted by screws 48 andspacers 49 to upwardly offset end portions 25 of the diverging membersof the bracket 26 aforedescribed. The spring arms carry contact points50 on their adjacent faces and are biased towards one another to providea substantial pressure to close the contact points. Secured to the endportions of the spring contact arms, as by spot-welding, are rigid roundextensions which extend past opposite sides of the shaft 32. The part ofthis shaft 32 between these extensions is hardened and ground down toform a smooth oval-shaped cam 52. Under the influence of the bias of thespring arms 44, the extensions 5| bear against this cam from theopposite sides thereof like the action lof a tweezers. However, toprevent the cam from shorting the contact points, the extensions aremade of Kovar and covered with a thin film of adhering glass 53. In theembodiment herein shown the cam 52 is so oriented in relation to thecoil 3| that when the coil is in zero position the major axis of the camis at right angles to the spring contact extensions 5|, with the tips ofthe cam in engagement with these extensions to hold the spring contactarms 44 at their maximum separation. 'I'he contact points 50 are nowheld spaced apart but only at a minimum distance required for dependablecircuit breaking. When the coil is current actuated from zero position,however, the tips of the cam move inward from the spring contactextensions and the contact points 50 are closed in response to the biasof the spring contact arms. This deflection of the coil is to be in aclockwise direction against the restraining force of the spiral springs4| and 42, the springs serving to restore the coil to zero position andto cam the spring contact arms apart when the current flow through thecoil is cut off.

Since the spring contact extensions engage the tips of the cam atsubstantially right angles to the major axis of the cam, these tipsserve as dwells against which the force of the spring contact arms isineffective to produce any deflection of the coil. The cam, being thusengaged by the spring contact extensions at an over-critical angle,serves as a one-Way power transferring means between the coil and thespring contact arms. In view of this over-critical condition of the camand the fact that it is wedged between the spring contact arms, theContact points are positively prevented against being closed by anymechanical vibration of the relay.

A further advantage in having the cam interposed between the springcontact arms to act against these arms in opposite directions is thatthe forces of the arms on the shaft of the coil are equalized and thereis no tendency to displace the coil pivots from its bearings, this beingparticularly important when a small movement is taken from the pivotedcoil because of the then relatively great reacting forces which areexerted on the coil shaft by the spring arms. Moreover, there is theparticularly important advantage that the separation of the contactpoints is independent of any lateral displacement which the pivots mayhave in their bearings. This permits the coil to be very freely pivoted,and eliminates the need for any critical adjustment of the bearingpressure against the pivots.

As typical values, the lengths of the maj or and minor axes of the cam52 may be .030" and .012"

respectively; and the minimum practical separation of the contactpoints-i. e., their maximum separation-may be .01" or less, preferablyabout .006". For these values, the contacts will close when the coil 3|is deflected approximately 60. Any deflection of the coil beyond thiscritical angle will thus cause the cam 52 to break contact with thespring arm extensions 5|, and to allow the full bias of the springcontact arms to be applied as pressure between the contact points. I donot, however, intend any unnecessary limitation of myinvention to theparticular critical angie here specified.

It will be seen that the work performed by the coil is utilized incharging the restoring springs 4| and 42 and in overcoming the camfriction. there being no work required c-f the coil to move the springcontact arms as the coil is deflected from zero position for these armsare now closing in response to their own biasing and effective actually,once the coil has been moved out of zero position, to aid in thedeflecting of the coil. The amount of work which the coil must storeinto the restoring springs must, however, be sufficient to enable therestoring springs to return the coil to zero position and cam the springcon`- tact arms back to open positions. Although the coil is capable ofexerting only a limited maximum torque, by adjusting the restoringsprings to allow the coil to be actuated through a large angle ofdeflection the coil is enabled to store an increased amount of energy inthese springs. Also, by` using a movement transmission having a smallmovement-transmitting ratiowhich is made possible by moving the coilthrough a maximum angle and the spring contact arms through a minimumseparation-what energy is stored in these springs is effective tocontrol an increased force between the spring contact arms. As a furtheraid in this direction there is the factor that an approximate matchoccurs between springr restoring force and cam load for the cam load onthe return stroke starts at a maximum but so also does the springrestoring force. While cam friction is a dissipation factor in thesystem, this friction is made small by having the engaging surfaces madesmooth, hard and of dissimilar materials. as is aforementioned.

The various factors abovementioned enable the small actuating torque ofa DArsonval movement to control a relatively great contact pressure. Asa typical example, I-have found that the contact points may be biasedtogether by as much as 11/2 grams force and be controlled by only 25microwatts of power fed into the coil.

It will be understood that where a self restoration of the relay is notan essential feature, the

restoring springs 4| and 42 may be arranged to exert no substantialreacting force on the coil 3| and the coil when once actuated will berestored to Zero position, or be reset, by hand in any suitable way. Inthis case, the contact pressure may be very much increased for the biasof the spring contact arms against the cam will need to be limited onlyby the amount of cam friction which the actuating torque of the coilwill have to overcome.

From the foregoing description, it is seen that the meter relay which Iprovide retains the sensitivity which is characteristic 0f this type ofrelay but is made very rugged inV construction. Moreover, it is seenthat the relay contact points are closed under a relatively greatcontact pressure, are substantially free from contact chatter and arenot susceptible to erratic operation in response to slight variations inactuating current or mechanical vibration. These factors make this relayhighly adapted for dependable service in applications where smallelectric powerl is available and where the operating conditions are notwell suited to sensitive meter relays as usually constructed. As atypical application, I have found that this relay is highly suited foruse in fire alarm systems on aeroplanes as the relay is sufficientlysensitive to be actuated by a thermocouple and is yet capable ofwithstanding the heavy vibration and changes in temperature to which theplane is subjected. There are of course many other applications for thisrelay where other sensitive meter relays of the usual form are wellnighprecluded.

The particular embodiment of my invention herein shown and describedwill be understood to be subject to many changes and modificationswithout departure from the true scope of my invention, which I endeavorto express according to the following claims.

I claim:

l. In a relay including an electric meter movement having a pivotedarmature that is deflected angularly upon supplying current to saidmovement: the combination of a switch including a pair of contactsrelatively movable through a range of the order of .01 to operate theswitch between open and closed conditions; and means,

operatively interposed between said armature and said switch andprogressively operated by said armature upon movement of the armaturethroughout at least the major part of a right angle, for progressivelymoving said contacts relaf tively to each other through said range tooperate said switch.

2. In a sensitive electrical relay comprising an electric meter movementhaving a pivoted armature that is deflected angularly from a zeroposition thereof upon supplying current to said movement, and a shaftfor said armature: the combination of a switch including a pair ofcantilever-mounted spring contact arms held in substantially parallelrelationship at opposite sides of said shaft and relatively movabletoward and away from each other to operate said switch between open andclosed conditions, said arms being biased toward one another; and a caminterposed between said arms and progressively operated by said shaftupon pivotal movement of said armature throughout a major fraction of aright angle for progressively moving said arms to operate said switchbetween open and closed conditions.

3. A meter relay adapted to withstand heavy vibration without erraticoperation comprising an electric meter movement having a pivotedarmature that is deflected angularly from a first to a second positionupon supplying current to said movement; means for returning saidarmature to said first position; a shaft for said armature; a switchincluding a pair of contacts and a pair of cantilever-mounted springarms at opposite sides of said shaft for carrying said contacts, saidspring arms being operable to move said contacts through a range of theorder of .01" to operate said switch between open and closed conditions;and a cam interposed between said arms and progressively operated bysaid shaft upon pivotal movement of said armature between said first andsecond positions for progressively moving said contacts through saidrange to operate said switch from one to the other of its saidconditions, said cam operating positively to hold said switch in onecondition when said armature is in one of said positions.

4. In a meter relay comprising an electric meter movement having apivoted armature that is deflected angularly from a zero position uponsupplying current to said movement, and a shaft for said armature: thecombination of a pair of cantilever-mounted spring arms at oppositesides of said shaft; a pair of cooperating electrical contacts mountedrespectively on adjacent sides of said arms, said arms being biased toyieldably hold said contacts closed; a cam secured to said shaft betweensaid arms and effective for positively holding said contacts apart by amaximum distance of the order of .01", said cam being oriented on saidshaft to hold said contacts apart by said distance when said armature isin zero position, and said cam being adapted to progressively releasesaid contacts into contact with each other in response to a deflectionof said armature through a substantial fraction of a right angle fromZero position; and spring means effective on said armature to return thesame to zero position and to open said contacts upon removal of thesupply of current to said electric meter movement.

5. In a relay comprising an electric meter movement having a pivotedarmature that is deflected angularly upon supplying current to saidmovement: the combination of a shaft for said armature; apair of contactarms biased together and disposed at opposite sides of an integralportion of said shaft, said integral portion being non-circular andeffective to cause the contacts of said arms to be moved into and out ofengagement with one another, through a maximum distance of the order of.01 or less, upon deflection of said armature.

FREDERICK G. KELLY,

